Blend of butadiene-styrene copolymer and butadiene-unsaturated heterocyclic nitrogen base copolymer and method of producing the cured product thereof



waited Thomas 3. Kennedy, Burger, Tex and John LHoist,

Boulder, (3010., assignors to Phillips Petroleum Comparry, a corporation of'Delaware No Drawing. Application May 13, 1957 Serial No. 658,522

8 Claims. (Cl. 260-455) This invention relates to synthetic rubber. In a further aspect, this invention relates to a method of preparing synthetic rubber having increased modulus'and to the products produced by the process.

A great many varieties ofsynthetic rubber are available to fabricators of rubber articles. A constant search is on to obtain articles of superior properties While decreasing the costs of components used therein. For one example, the accelerators used in curing synthetic rubber are expensive and attempts have been made to reduce the amounts used. However, when the amount is reduced, the properties of the product, particularly the modulus, are impaired. In the polymerization systems, attempts have been madeto use cheaper emulsifying agents, such as tall o'il soaps but it has been found that the polymers produced with such recipes have a slow curing rate.

We have discovered that the curing rate can be increased by incorporating in certain types of synthetic rubber a small amount of a polymer prepared from a copolymerizableheterocyclic nitrogen base. By so doing, the amount of accelerationcan be reduced while still obtaining a good cure. Also, the cheap tall oil soap can be used in the polymerization recipe. A specific example of the composition covered by thepresent invention is a rubbery butadiene/styrene copolymer to which has been added a small amount of a butadiene/Z-methyl- S-vinylpyridine copolymer. Amounts of the second copolymer as low as one percent bring about a very decided increase in modulus of the product when compared to the same copolymer without the added material.

The following are objects of the present invention.

An object of this invention is to provide new rubber compositions. A further object of this invention is to permit the use of cheap emulsifying agents While producing rubber of good quality. A further object of this invention is to permit reduction in accelerator level in rubber compounding recipes. A further object of this invention is to provide synthetic rubbery compositions having increased modulus.

Other objects and advantages of this invention will become apparent to one skilled in the art upon reading the accompanying disclosure.

As stated, our invention is'based upon the discovery Patented July 7, 1959 that a small amount of a rubbery polymer prepared by polymerizing a minoramount'of a copolymerizable heterocyclic nitrogen base with a major amount; of a conjugated diene, when added to a synthetic rubber, will provide a considerable increase in modulus of the product and will provide a product having good physical properties. The base rubbers in which this improvement is to be found are those prepared by polymerizing a major amount of a conjugated diolefin containing not over 6 carbon atoms and a=minor amount of styrene, alphamethyl styrene, vinyl toluene, acrylonitrile, methacrylonitrile, ethacrylonitrile,-methyl 'acrylate, or ethyl acrylate. These rubbers are generally known as the butadiene/styrene type, the nitrile type, and the acrylate type. The dienes used in this polymerization include 1,3-

butadiene, isoprene, piperylene, methyl pentadiene, and 2,3-dimethyl 1,3-butadiene. The copolymerizable heterocyclic nitrogen bases are those of the pyridine and quinoline series, including'the isoquinolines, which contain a CHFC group wherein- R is hydrogen or methyl. Alkyl groups arealso present on-the-nucleus although the total number of carbon-atoms'i-n all of the -alkyl groups should not be greater than '12. Representative'heterocyclic nitrogen compounds usefulinthe practice of this invention include: 'Z-VinylpyIidine; 2-methyl-S-vinylpyridine; 5- methyl Z-vinylpyridine; 3 ethyl 5 vinylpyridine; 5-ethyl=2- vinylpyridin'e; '4-methyl 3'-vinylpyridine; 2,3,4-trimeth'yl- S-VinyIpyridine; '2',5-'divinylpyridine; 2-isopropenylpyridine; 5-p'ropyl-2-isopropenylpyridine; 2-octyl-5-vinylpyridine; Z-Vinylquinoline; 8-ethyl-2-vinylquinoline; 4-heXyl- S-vinylquinoline; l-vinyl-isoquinoline; S-methyl-l-isopro penylisoquinoline; and the like. These copolymers which are added to the base rubber are prepared by polymerizing a minor amount of the substituted pyridine or quinoline with a major amount of a conjugated diene containing not over 6 carbon atoms, examples of which are the same as set forth above. Only a small amount of the rubbery nitrogen containing copolymer is used, the greatest effect being noted when up to 5 percent'by weight .is used based upon the Weight of the base rubber. In general, 1 to 3 percent is sufiicient to obtain the desired eifect, this amount being generally used with the preferred nitrogen containing additives, i.e., those prepared by polymerizing 85 to percent by weight of butadiene with 15 to 25 percent by weight of 2-methyl- 5-vinylpyridine. In general, the amount of this nitrogen containing polymer to be added should besu'ch that 0.001 to-0.3 weight percent of the final product is nitrogen.

Many methods of polymerization can be used in the production'of the two copolymers which'form the product of our invention but we prefer to use-emulsion poly- 3 merization systems, many examples of which are shown in Synthetic Rubber, by Whitby.

The method of mixing of the two copolymers does not afiect the product obtained to any great extent. We

The 2-methyl-5-vinylpyridine rubber was used in amounts from 0.1 weight percent to 4.0 weight percent based upon the butadiene/styrene rubber. Following mixing, each mixture was compounded using the followhave mixed these polymers in latex form and on the 5 ing recipe: mill. It is frequently more convenient in the process Parts by Welght Rubber 100 to rmx the two materials in latex form where both ma- B1 ack (EPC) 40 tenals are prepared in the same plant. However, mill Zinc oxide 5 mixing is of greater utility wherein a rubber product Sulfur 2 manufacturer wishes to obtain the advantage of our in- ZLdibenzothiazfl 3 ven ion. Stearic acid 1.5 The following examples Illustrate our mventlon' Following compounding of the recipes, the specimens EXAMPLE I were cured for 2 5, 50, and 100 minutes at 292 F. and tested to determine modulus, tensile strength, and elon- A butadiene/ styrene copolymer was prepared by emulgation. The results are shown in Table I.

Table I Bugadienel 23%??? R gd Modulus Tensile (p.s.l.) Elongation (Percent) 11 V aw wi gl yrlid ine may 532E3 3 5 par s y cope met, 2 we pgg isgg y mm. 121 31. 102. 111 11. 11%. 151 12. 111 31. 100 0 58.5 400 000 1,420 4,000

% & 2: p5 1,540 3,000 4,040 3,700 850 228 510" 100 M0 800 1,410 HQ 2,58 4,050 4,150 800 020 510 100 1.00 61.0 930 1,570 1,930 4,080 3,860 3,690 720 650 470 100 no mo 1 240 2,010 2,280 4,270 900 3,420 680 500 420 100 4.00 00.0 1:500 2:140 2'000 ssao s' 2 3% 22 0 0 100 50.5 ,320 1,010 11790 21050 430 sion polymerization at 40 F. using the following recipe. EXAMPLE 11 Parts by weight Butadiene 7Z0 Uslng the same butadlene/styrene copolymer, addi- Styrene 2& tlonal runs were made using a butadiene/Z-methyl-S- Water 190.0 vinylpyridine prepared by emulsion polymerization at Rosin s ap, K salt F. and taken to 90% conversion using the following Potassium chloride 0,40 recipe: Tamol N 1 0.15 Versene 2 0.01 Parts by weight Sodium hydroxide 0.04 Butadiene 35 Tert-d y mercaptan 2-methyl-5-vinylpyridine 15 FeSO 7H O 010 Water 230 Potassium pyrophosphate 0.253 K fatt y acid soap 6.0 Para-menthanehydroperoxlde 0.125 P t hl Sodium dimethylditbiocarbamate 0.100 Oasslumf e S0dlum salt of a naphthalene sulfonlc acid condensed Tamol N 0.3 with formaldehyde. Versene 1 0.06

Ethylene diamine tetracettc acid.

Tert-dodecyl mercaptan Variable After conversion, the rubber was coagulated and F errous sulfate heptahydrate 0.04 mixed on the mill wlth a but-adiene/Z-methyl-S-vmyl- P h h pyridine rubber prepared by emulsion polymerization at 60 ane ydroperoxl e 40 F. and taken to 60% conversion using the following Sodlum formaldehyde Sulfoxylate recipe: 1 See Example I.

Parts by weight Butadiene 75 Methylvinylpyridine 25 I To the latex of the butad ene/ styrene copolymer, sulfiwater 230 cient latex of the butad1ene/2-methyl-5-v1nylpyr1d1ne K Fatty acid soap 6.0 polymer was added to give 1.8 percent by weight of the Potassium chloride 0.5 butadiene/2-methyl-5-vinylpyridine rubber based upon Tamol N the butadiene/styrene copolymer. The mixture of the Verseml latices was coagulated and the rubber compounded ac- Tert'docecyl mercaptan cording to the recipe of Example I and cured at 292 F. Ferrous sulfate heptahydrate 0.04

for 25, 50, and 100 mlnutes. As in Example I, portlons Para-menthanehydroperoxlde 0.10 d d th Sodium f ld h d smoxylate 040 of this mixture were teste to etermme e pr p r s I Seeabove recipe. thereof, these properties being set forth m Table H.

Table II Butadiene/ 300% Modulus Tensile (p.s.i.) Elongation (Percent) Butadiene/ 2-methyl-5- Comstyrene vinyl Raw pounded copolymer, pyridine Mooney Mooney parts by copolymer, (ML-4) (ML-4) 25 50 100 25 50 100 2 5 50 100 weight parts by min. min. min. min. min. mm. mm. mm. min.

weight EXAMPLE III copolymer being suflicient to provide 0.001 to 0.3 weight The butadiene/Z-methyl--vinylpyridine copolymer of Example I was mixed with the butadiene/styrene copolymer of Example I in an amount of 4 percent based on the butadiene/styrene copolymer. The compounding recipe of Example I Was used except that the accelerator Was omitted. After one hour at 292 F., no curing was apparent. Thus, the 2-methyl-5vinylpyridine component, while giving a large increase in cure, does not function as a cure accelerator.

We claim:

1. A rubber composition comprising a rubbery copolymer prepared by polymerizing a major amount of a conjugated diene containing not over 6 carbon atoms and a minor amount of a monomer selected from the group consisting of styrene, alpha'methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, ethylacrylonitrile, methyl acrylate, and ethyl acrylate; and a small quantity of a second polymer prepared by polymerizing a major amount of a conjugated diene containing not over 6 carbon atoms and a minor amount of a copolymerizable CHQ=(I} substituted heterocyclic nitrogen base of the pyridine and quinoline series Where R is selected from the group con sisting of hydrogen and methyl, the amount of said second polymer being sufiicient to provide 0.001 to 0.3 weight percent nitrogen based upon the total weight of the polymers in the composition.

2. A rubber composition comprising a rubbery butadiene/ styrene copolymer and a small quantity of a butadiene/2-methyl-5-vinylpyridine copolymer, the amount of said butadiene/Z-methyl-S-vinylpyridine copolymer being suflicient to provide 0.001 to 0.3 weight percent nitrogen based upon the total Weight of the polymers in the composition.

3. A rubber composition comprising a rubbery butadiene/styrene copolymer and a small amount not exceeding 5 percent by Weight of a butadiene/Z-methyl-S- vinylpyridine copolymer.

4. A molded and vulcanized rubber composition comprising 25 to 75 parts of carbon black per 100 parts of synthetic rubber, the synthetic rubber component being a rubbery butadiene/ styrene copolymer and a small quantity of a butadiene/2-methyl-5-vinylpyridine copolymer, the amount of said butadiene/Z-methyl-S-vinylpyridine percent nitrogen based upon the total weight of the polymers in the composition.

5. A molded and vulcanized rubber composition comprising 25 to parts of carbon black per parts of synthetic rubber, the synthetic rubber component being a rubbery butadiene/styrene copolymer and a small quantity not exceeding 5 percent by Weight of a butadiene/2-methyl-5-vinylpyridine copolymer.

6. The method of producing a cured rubbery copolymer of increased modulus, said rubbery copolymer prepared by polymerizing a major amount of a conjugated diene containing not over 6 carbon atoms and a minor amount of a monomer selected from the group consisting of styrene, alpha-methylstyrene, vinyltoluene, acrylonitrile, methylacrylonitrile, ethacrylonitrile, methyl acrylate, and ethyl acrylate, comprising adding a small quantity of a second polymer prepared by polymerizing a major amount of a conjugated diene containing not over 6 carbon atoms and a minor amount of a copolymerizable OHS-:0-

substituted heterocyclic nitrogen base of the pyridine and quinoline series where R is selected from the group hydrogen and methyl, and curing the resulting mixture, the amount of said second polymer being sufficient to provide 0.001 to 0.3 weight percent nitrogen based upon the total weight of the polymers in the composition.

7. The method of producing a cured rubbery buta diene/ styrene copolymer of increased modulus which comprises mixing With said copolymer a small quantity of a rubbery butadiene/2-methyl-5-vinylpyridine copolymer and curing the resulting composition, the amount of said butadiene/Z-methyl-S-vinylpyridine copolymer being sufli cient to provide 0.001 to 0.3 Weight percent nitrogen based upon the total weight of the polymers in the composition.

8. The method of producing a cured rubbery butadiene/ styrene copolymer of increased modulus which comprises mixing With said copolymer a small quantity not exceeding 5 percent by weight of a rubbery butadiene/2- methyl-S-vinylpyridine copolymer and curing the resulting composition.

References Cited in the file of this patent Whitby: Synthetic Rubber, John Wiley & Sons Inc. 183w York), 1954, pages 725-726. 

1. A RUBBER COMPOSITION COMPRISING A RUBBERY COPOLYMER PREPARED BY POLYMERIZING A MAJOR AMOUNT OF A CONJUGATED DIENE CONTAINING NOT OVER 6 CARBON ATOMS AND A MINOR AMOUNT OF A MONOMER SELECTED FROM THE GROUP CONSISTING OF STYRENE, ALPHA-METHYLSTYRENE, VINYLTOLUENE, ACRYLONITRILE, METHACRYLONITRILE, ETHYLACRYLONTRILE, METHYL ACRYLATE, AND ETHYL ACRYLATE; AND A SMALL QUANTITY OF A SECOND POLYMER PREPARED BY POLYMERIZING A MAJOR AMOUNT OF A CONJUGATED DIENE CONTAINING NOT OVER 6 CARBON ATOMS AND A MINOR AMOUNT OF A COPOLYMERIZABLE 